Eight sections of Cenomanian Chalk from Southern England have been examined for their Ostracoda. A total of 111 species and 3 sub-species have been found and these fall into 47 genera. 38 of these species have been previously described, 47 are new and the r e s t have been left under open nomenclature. A generalised distribution chart for some of the more important species has been drawn up and the distribution of species in each individual section has been compared to this chart. As a result it can be seen that Ostracoda can be very useful in stratigraphic work in the Cenomanian. Their stratigraphy has been related to the macrofossil zonations and in particular to the Foraminiferal zonation. The Ostracoda indicate that normal marine salinities prevailed throughout the Cenomanian period in Southern England and that temperatures were probably in excess of 10°C. Distinct changes in the ostracod fauna during the Cenomanian may be due in part to an increasing temperature but some of the changes appear to be related to an increase in sea depth. The presence of numerous small specimens in the Middle and Upper Cenomanian may indicate very quiet conditions of deposition during which oxygen levels were reduced. The ostracod fauna from Southern England has more affinity to the fauna described from the eastern part of the Paris Basin and the southern Alpine region of France than with other areas in France.

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